Magnetic system

ABSTRACT

A magnetic system comprising an annular, axially magnetized, permanent main magnet, engaging on either end a soft iron plate; at the center of the main magnet and between the plates a soft iron core is arranged so as to be surrounded, with an airgap formed by one plate and said core, while on at least one of the plates an auxiliary magnet is provided which is magnetized mainly in the opposite direction of stray external magnetic flux.

United States Patent 306; 17911155 SF,117.12O

[56] References Cited UNITED STATES PATENTS 3.067366 12/1962 Hofman 7, 179/117 X FOREIGN PATENTS 1,076,838 3/1960 Germany 179/1 15.5 106,l58 l/l963 Czechoslovakia 335/231 Primary Examiner-G. Harris Attorney-Frank R. Trifari ABSTRACT: A magnetic system comprising an annular, axially magnetized, permanent main magnet, engaging on either end a soft iron plate; at the center of the main magnet and between the plates a soft iron core is arranged so as to be surrounded, with an airgap formed by one plate and said core, while on at least one of the plates an auxiliary magnet is provided which is magnetized mainly in the opposite direction of stray external magnetic flux.

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WYTZE HCFMAN BY AGENT PATENTEUJUUIHQ?! 3.593.239

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WYTZE HOFMAN GENT MAGNETIC SYSTEM Such a device is known from British Patent Specification 927,545, corresponding to U.S. Pat. No. 3,067,366 which describes a magnetic system for use in a loudspeaker. The annular main magnet is provided with an upper plate and a lower plate, the latter being engaged by a disc-shaped auxiliary magnet. The auxiliary magnet has a smaller diameter than the main magnet and the plates.

Although the auxiliary magnet considerably reduces the external stray field, it has been found necessary in practice to atrange the assembly in a soft iron pot so that the external stray field disappears substantially completely.

The invention is characterized in that the auxiliary magnet completely covers the plate and surrounds it, the direction of magnetization of the auxiliary magnet being adapted to the shape of the plate and being at right angles to the surface thereof.

Object of the invention is to provide an absolutely stray-free magnetic system without the need for arranging the system in a pot. Such a magnetic system can therefore by manufactured in a very simple manner. The auxiliary magnet is separately manufactured in the form of a hood, which is simply slipped onto the associated plate when mounted.

The auxiliary magnet suppresses not only the external stray field but it also enhances the useful flux in the airgap. If this is not desired, the annular main magnet may be smaller, which involves a considerable saving of costs, since the manufacturing costs, or example, of oxideceramic magnets increase more than proportionally to the average diameters of these magnets.

An embodiment of the invention is characterized in that the plate has a conical sectional area, while the auxiliary magnet formed like a hood matches the conical shape of the plate. The conical plate may be punched very easily from sintered iron sheet.

It has been found that without involving alteration of the useful flux in the airgap and of the external stray field the cylindrical portion of the auxiliary magnet may be provided with one or more cavities or holes. In this way a fairly considerable economy of material is obtained.

The invention will be described more fully with reference to a drawing. In this drawing FIG. I is a cross-sectional view of a magnetic system comprising a lower plate with an auxiliary magnet,

FIG. 2 is a cross-sectional view of a magnetic system having an upper plate with an auxiliary magnet,

FIGS. 3 and 4 are cross-sectional views of a magnetic system having an upper plate and a lower plate with an auxiliary magnet,

FIG. 5 is a cross-sectional view of a magnetic system having a conical lower plate with an auxiliary magnet,

FIG. 6 is a erspective view of separate components of the magnetic system of FIG. 5.

FIGS. 7, 8 and 9 are cross-sectional views of a magnet system comprising an auxiliary magnet in various embodiments.

The magnetic system shown in FIGS. 1 to 5 comprises an axially magnetized annular magnet I of oxide-ceramic material having an annular upper plate 2 and a disc-shaped lower plate 3 both of soft iron. The lower plate 3 is provided with a soft iron core 4, which forms the useful airgap 5 with the upper plate 2. The lower plate of FIG. I is provided with an elastic auxiliary magnet 6. whose edge 7 fits intimately around the lower plate 3. Thus the external magnetic field disappears with the exception of the close proximity of the useful airgap.

The upper plate 2 of FIG. 2 is provided with an annular auxiliary magnet B, which completely grips around the upper plate 2. By this auxiliary magnet the external magnetic field. especially in the neighborhood of the useful airgap is drastically reduced.

FIGS. 3 and 4 show a combination of the embodiments shown in FIGS. 1 and 2. Both systems have practically no extemal magnetic field. The hood-shaped auxiliary magnet 6 of FIG. 3 is formed by an oxide-ceramic disc 9, magnetized axially in the opposite direction and by a ring 10 of elastic magnetic material clamping around the disc 9 and the lower plate 3. The upper plate 8 of FIG. 4 is thickened on the inner side I I in order to reduce further the stray field.

The lower plate! of FIG. 5 is pressed in a conical shape from a sintered iron sheet. The auxiliary magnet 6 consists of a flexible synthetic resin mixed with ceramic, magnetic powder. It is formed by a disc which is secured by an adhesive to the bottom side of the lower plate 3.

The components of this magnetic system are shown In FIG. 6 ina perspective view. As shown in FIGS. 7, 8 and 9 the auxiliary magnet 6, particularly the cylindrical portion 9 covers partly the baseplate 3. The auxiliary magnet 6 of FIG. 7 is annular and has a cylindrical hole 12. The cylindrical portion 9 of FIG; 8 has a cavity 13 adjacent the base plate 3. The cylindrical portion 9 of FIG. 9 has a plurality of holes 14.

I claim:

I. A magnetic system comprising,

an annular, axially magnetized, permanent main magnet having first and second ends;

a first plate of soft ferromagnetic material having an inner side disposed adjacent one end of the main magnet and an outer exposed side and edges, and a second similar plate disposed adjacent the opposite end of the permanent magnet;

a soft ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and the second plate;

first auxiliary permanent magnet means disposed adjacent at least one of said two plates and this auxiliary magnet generally surrounding and in intimate contact with and covering only said exposed side and edges of the first plate and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray tlux of the main magnet where the auxiliary magnet contacts said plate;

a second auxiliary, permanent magnet generally similar to the first and disposed similarly adjacent the second plate.

2. A magnetic system comprising,

an annular, axially magnetized, permanent main magnet formed as a circular cylinder having first and second ends;

a first plate formed as a solid disc of sofl ferromagnetic material having an inner side disposed adjacent the first end of the main magnet and an outer exposed side and edges, and a second plate formed as a ring with an aperture defining an inner edge, disposed adjacent the second end of the permanent magnet;

a soft ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and said inner edge of the second plate;

first auxiliary permanent magnet means formed as a cylinder with a central aperture disposed adjacent said first plate and this auxiliary magnet generally surrounding and in intimate contact with only the peripheral portions of said exposed side and edges of the first plate, and terminating at the junction of the first end of said main magnet and the first plate, and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray flux of the main magnet where the auxiliary magnet contacts said plate.

3. A magnetic system comprising,

an annular, axially magnetized. permanent main magnet having first and second ends;

a first plate of soft ferromagnetic material having an inner side disposed adjacent one end of the main magnet and an outer exposed side and edges, and a second similar plate disposed adjacent the opposite end of the permanent magnet, one of said plates being generally conical in cross section;

a sofi ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and the second plate; first elastic auxiliary permanent magnet means disposed adjacent the conical plate and conforming to the shape thereof, and generally surrounding and in intimate contact with only said exposed side and edges of the plate, and terminating at the junction of said first end of the main magnet and said first plate, and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray flux of the main magnet where the auxiliary magnet contacts said plate.

4. A magnetic system comprising an annular, axially magnetized. permanent main magnet engaging on either side a soft iron plate, at the center of the main magnet a soft iron core is arranged so as to be surrounded by the main magnet and one plate. the other plate forming together with the core the useful airgap, while at least one of the plates is provided with an auxiliary magnet formed as an axially magnetized cylinder with a radially magnetized disc closing one end, and thus magnetized substantially in the opposite direction as the adjacent main magnet, characterized in that the auxiliary magnet substantially completely covers one of said plates and generally surrounds the same, said auxiliary magnet being in intimate contact with an exposed side of said plate and having a flange portion in intimate contact with edges of said plate and terminating at the junction of said plate and main magnet, the direction of magnetization of the auxiliary magnet matching the shape of the plate and being at right angles to the surface thereof.

5. A magnetic system according to claim 3 wherein the auxiliary magnet comprises an elastic synthetic resin including therein a permanent magnetic power and corresponds in shape to the adjacent plate. 

1. A magnetic system comprising, an annular, axially magnetized, permanent main magnet having first and second ends; a first plate of soft ferromagnetic material having an inner side disposed adjacent one end of the main magnet and an outer exposed side and edges, and a second similar plate disposed adjacent the opposite end of the permanent magnet; a soft ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and the second plate; first auxiliary permanent magnet means disposed adjacent at least one of said two plates and this auxiliary magnet generally surrounding and in intimate contact with and covering only said exposed side and edges of the first plate and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray flux of the main magnet where the auxiliary magnet contacts said plate; a second auxiliary, permanent magnet generally similar to the first and disposed similarly adjacent the second plate.
 2. A magnetic system comprising, an annular, axially magnetized, permanent main magnet formed as a circular cylinder having first and second ends; a first plate formed as a solid disc of soft ferromagnetic material having an inner side disposed adjacent the first end of the main magnet and an outer exposed side and edges, and a second plate formed as a ring with an aperture defining an inner edge, disposed adjacent the second end of the permanent magnet; a soft ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and said inner edge of the second plate; first auxiliary permanent magnet means formed as a cylinder with a central aperture disposed adjacent said first plate and this auxiliary magnet generally surrounding and in intimate contact with only the peripheral portions of sAid exposed side and edges of the first plate, and terminating at the junction of the first end of said main magnet and the first plate, and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray flux of the main magnet where the auxiliary magnet contacts said plate.
 3. A magnetic system comprising, an annular, axially magnetized, permanent main magnet having first and second ends; a first plate of soft ferromagnetic material having an inner side disposed adjacent one end of the main magnet and an outer exposed side and edges, and a second similar plate disposed adjacent the opposite end of the permanent magnet, one of said plates being generally conical in cross section; a soft ferromagnetic core extending from the first plate through the bore of the main magnet toward the second plate with an airgap established between the core and the second plate; first elastic auxiliary permanent magnet means disposed adjacent the conical plate and conforming to the shape thereof, and generally surrounding and in intimate contact with only said exposed side and edges of the plate, and terminating at the junction of said first end of the main magnet and said first plate, and disposed in at least a portion of the usual path of external stray magnetic flux, the direction of magnetization of the auxiliary magnet being generally opposite the direction of magnetization of said stray flux of the main magnet where the auxiliary magnet contacts said plate.
 4. A magnetic system comprising an annular, axially magnetized, permanent main magnet engaging on either side a soft iron plate, at the center of the main magnet a soft iron core is arranged so as to be surrounded by the main magnet and one plate, the other plate forming together with the core the useful airgap, while at least one of the plates is provided with an auxiliary magnet formed as an axially magnetized cylinder with a radially magnetized disc closing one end, and thus magnetized substantially in the opposite direction as the adjacent main magnet, characterized in that the auxiliary magnet substantially completely covers one of said plates and generally surrounds the same, said auxiliary magnet being in intimate contact with an exposed side of said plate and having a flange portion in intimate contact with edges of said plate and terminating at the junction of said plate and main magnet, the direction of magnetization of the auxiliary magnet matching the shape of the plate and being at right angles to the surface thereof.
 5. A magnetic system according to claim 3 wherein the auxiliary magnet comprises an elastic synthetic resin including therein a permanent magnetic power and corresponds in shape to the adjacent plate. 